The endocannabinoid system plays a critical role in several diseases, including drug dependence. The long-term objective of this application is to understand the role that CB1, CB2 and orphan G-protein-coupled receptors play in these processes. Presently, CB1 receptor agonists act both centrally and peripherally and as well as at CB2 receptors. We propose to develop new CB1 receptor agonists that lack CB2 receptor affinity and/or are restricted to the periphery. Considerable emphasis will be placed on CB1 receptor allosteric modulators as we predict they will produce a pharmacological profile distinct from orthosteric ligands. Furthermore, perturbation of the endocannabinoid system in disease states could be due to either alterations in endocannabinoid levels or constitutive receptor activity, processes that are not easily distinguished by current CB1 receptor inverse agonists/antagonists. Therefore, we will pursue new leads in developing neutral CB1 receptor antagonists that will act solely to block endocannabinoids. Since both CB1 and CB2 receptors exhibit anti-inflammatory and analgesic properties, we propose to fully characterize these properties of CB2 selective agonists that we developed during the current funding period. In addition, we will determine the degree of tolerance that these CB2 selective agonists produce. There is now ample evidence that additional cannabinoid receptor subtypes exist, including several orphan G-protein-coupled receptors. One of our goals is to determine whether GPR55 is a cannabinoid receptor, and if so, what is its pharmacological properties and contribution to drug dependence. Based upon many years of experience, we have developed an evaluation screen that allows us to prioritize new compounds for analysis. Initial evaluation in CB1 and CB2 receptor binding and function assays allow us to determine which compounds will be evaluated in vivo using the mouse tetrad or in situ using smooth muscle preparations. Subsequent analysis will include acute and chronic pain models, drug discrimination, tolerance and dependence protocols as appropriate for individual specific aims. We will also employ CB1, CB2, and GPR55 knockout mice as necessary. New cannabinoid orthosteric agonists and allosteric modulators for CB1, CB2 and new cannabinoid receptors, as well as neutral antagonists, hold promise as therapeutic agents for treatment of drug dependence, chronic pain, and other neurological disorders. PUBLIC HEALTH RELEVANCE: The goal of this project is to gain a better understanding of the role that the endocannabinoid system plays in pain perception and drug addiction. We propose to develop new drugs for investigating the endocannabinoid system. These drugs will also have potential use as analgesics and drug abuse medications.